WebDAV: fixed Google throttling workaround during initial sync

The "retry on 401" code wasn't active during the initial sync
because the fact that the credentials had been accepted before
was only recorded on disk, but not in memory.

src/backends/webdav/WebDAVSource.cpp

@@ -146,6 +146,7 @@ public:
             boost::shared_ptr<FilterConfigNode> node = m_context->getNode(WebDAVCredentialsOkay);
             WebDAVCredentialsOkay.setProperty(*node, okay);
             node->flush();
+            m_credentialsOkay = okay;
         }
     }